The jet nozzles were originally designed to swivel downwards for shorter takeoffs and landings. This feature was initially included on prototype aircraft, but was removed from the design during flight testing. The cockpit used an unusual double pane windscreen and side-by-side seating arrangement in which the pilot sat in the left seat, while the bombardier/navigator sat to the right and slightly below. The incorporation of an additional crew member with separate responsibilities, along with a unique cathode ray tube (CRT) display that provided a synthetic display of terrain ahead, enabled low-level attack in all weather conditions.

The A-6's wing was very efficient at subsonic speeds compared to supersonic fighters such as the McDonnell Douglas F-4 Phantom II, which are also limited to subsonic speeds when carrying a payload of bombs. The wing was also designed to provide good maneuverability with a sizable bomb load. A very similar wing would be put on pivots on Grumman's later supersonic swing-wing Grumman F-14 Tomcat, as well as similar landing gear.[6] The Intruder was also equipped with the "Deceleron", a type of airbrake on the wings with two panels that opened in opposite directions; in this case, one panel went up, while another went down.

For its day, the Intruder had surprisingly sophisticated avionics (electronics systems), with a high degree of integration. It was felt that this could lead to extraordinary maintenance requirements, to identify and isolate equipment malfunctions. Hence, the aircraft was provided with automatic diagnostic systems, some of the earliest computer-based analytic equipment developed for aircraft. These were known as Basic Automated Checkout Equipment, or BACE (pronounced "base"). There were two levels, known as "Line BACE" to identify specific malfunctioning systems in the aircraft, while in the hangar or on the flight line; and "Shop BACE", to exercise and analyze individual malfunctioning systems in the maintenance shop. This equipment was manufactured by Litton Industries. Together, the BACE systems greatly reduced the Maintenance Man-Hours per Flight Hour, a key index of the cost and effort needed to keep military aircraft operating.

The Intruder was equipped to carry and launch a nuclear bomb and Navy crews regularly planned for assigned nuclear missions. Because the A-6 was a low-flying attack aircraft, an unusual method was developed for launching an atomic bomb, should that ever be required. Known as LABS-IP (Low Altitude Bombing System – Inverted Position) it called for a high-speed low-level approach. Nearing the target point, the pilot would put the aircraft into a steep climb. At a computer-calculated point in the climb, the weapon would be released, with momentum carrying it upwards and forwards. The pilot would continue the climb even more steeply, until near a vertical position the aircraft would be rolled and turned, heading back in the direction from which it came. It would then depart from the area at maximum acceleration. During this time, the bomb would rise to an apex, still heading in its original direction, then begin to fall towards the target while traveling further forward. At a pre-programmed height, it would detonate. By that time, the Intruder would be several miles away, traveling at top speed, and thus able to stay ahead of the shock wave from the explosion. This unusual maneuver was known as an "over the shoulder" bomb launch.

The Intruder received a new standardized US DOD designation of A-6A in the Autumn of 1962, and entered squadron service in February 1963. The A-6 became both the U.S. Navy's and U.S. Marine Corps's principal medium and all-weather/night attack aircraft from the mid-1960s through the 1990s and as an aerial tanker either in the dedicated KA-6D version or by use of a buddy store (D-704). Whereas the A-6 fulfilled the USN and USMC all-weather ground-attack/strike mission role, this mission in the USAF was served by the Republic F-105 Thunderchief and later the F-111, the latter which also saw its earlier F-111A variants converted to a radar jammer as the EF-111 Raven, analogous to the USN and USMC EA-6B Prowler.

A U.S. Marine Corps A-6 Intruder destroyed by a rocket and mortar bombardment on Danang Air Base during Vietnam war

A-6 Intruders first saw action during the Vietnam War, where the craft were used extensively against targets in Vietnam. The aircraft's long range and heavy payload (18,000 pounds or 8,200 kilograms) coupled with its ability to fly in all weather made it invaluable during the war. However, its typical mission profile of flying low to deliver its payload made it especially vulnerable to anti-aircraft fire, and in the eight years the Intruder was used during the Vietnam War, the U.S. Navy and U.S. Marine Corps lost a total of 84 A-6 aircraft of various series. The first loss occurred on 14 July 1965 when an Intruder from Attack Squadron 75 (VA-75) from the carrier USS Independence, flown by LT Donald Boecker and LT Donald Eaton, commenced a dive on a target near Laos. An explosion under the starboard wing damaged the starboard engine, causing the aircraft to catch fire and the hydraulics to fail. Seconds later the port engine failed, the controls froze, and the two crewmen ejected. Both crewmen survived.

Of the 84 Intruders lost to all causes during the war, ten were shot down by surface-to-air missiles (SAMs), two were shot down by MiGs, 16 were lost to operational causes, and 56 were lost to conventional ground fire and AAA. The last Intruder to be lost during the war was from Attack Squadron 35 (VA-35), flown by LT C. M. Graf and LT S. H. Hatfield, from the carrier USS America; they were shot down by ground fire on 24 January 1973 while providing close air support. The airmen ejected and were rescued by a Navy helicopter. Twenty U.S. Navy aircraft carriers rotated through the waters of Southeast Asia, providing air strikes, from the early 1960s through the early 1970s. Nine of those carriers lost A-6 Intruders: USS Constellation lost 11, USS Ranger lost eight, USS Coral Sea lost six, USS Midway lost two, USS Independence lost four, USS Kitty Hawk lost 14, USS Saratoga lost three, USS Enterprise lost eight, and USS America lost two.[7] Although capable of embarking aboard aircraft carriers, most U.S. Marine Corps A-6 Intruders were shore based in South Vietnam at Chu Lai and Da Nang and in Nam Phong, Thailand.

A-6 Intruders were later used in support of other operations, such as the Multinational Force in Lebanon in 1983. On 4 December, one LTV A-7 Corsair II and one Intruder were downed by Syrian missiles. The Intruder's pilot, Lieutenant Mark Lange, and bombardier/navigator Lieutenant Robert "Bobby" Goodman ejected immediately before the crash;[8] Lange died of his injuries while Goodman was captured and taken by the Syrians to Damascus where he was released on 3 January 1984. Later in the 1980s, two Naval Reserve A-7 Corsair II light attack squadrons, VA-205 and VA-305, were reconstituted as medium attack squadrons with the A-6E at NAS Atlanta, Georgia and NAS Alameda, California, respectively.

During Operation Desert Storm in 1991, U.S. Navy and U.S. Marine Corps A-6s flew more than 4,700 combat sorties, providing close air support, destroying enemy air defenses, attacking Iraqi naval units, and hitting strategic targets. They were also the U.S. Navy's primary strike platform for delivering laser-guided bombs.[9] The U.S. Navy operated them from the aircraft carriers Saratoga, John F. Kennedy, Midway, Ranger, America and Theodore Roosevelt, while U.S. Marine Corps A-6s operated ashore, primarily from Shaikh Isa Air Base in Bahrain. Three A-6s were shot down in combat by SAMs and AAA.[10]

The Intruder's large blunt nose and slender tail inspired a number of nicknames, including "Double Ugly", "The Mighty Alpha Six", "Iron Tadpole" and also "Drumstick".[11]

Following Desert Storm, Intruders were used to patrol the no-fly zone in Iraq and provided air support for U.S. Marines during Operation Restore Hope in Somalia. The last A-6E Intruder left U.S. Marine Corps service on 28 April 1993.[12]

Despite the production of new airframes in the 164XXX Bureau Number (BuNo) series just before and after Operation Desert Storm, augmented by a rewinging program of older airframes, the A-6E and KA-6D were quickly phased out of service in the mid-1990s in a U.S. Navy cost-cutting move driven by the Office of the Secretary of Defense to reduce the number of different type/model/series (T/M/S) of aircraft in carrier air wings and U.S. Marine aircraft groups.

Many in the US defense establishment in general, and Naval Aviation in particular, questioned the wisdom of a shift to a shorter range carrier-based strike force, as represented by the Hornet and Super Hornet, compared to the older generation aircraft such as the Intruder and Tomcat. However, the availability of USAF Boeing KC-135 Stratotanker and McDonnell Douglas KC-10 Extender tanking assets modified to accommodate USN, USMC and NATO tactical aircraft in all recent conflicts was perceived by certain senior decision makers in the Department of Defense to put a lesser premium on organic aerial refueling capability in the U.S. Navy's carrier air wings and self-contained range among carrier-based strike aircraft. Although the Intruder could not match the F-14's or the F/A-18's speed or air-combat capability, the A-6's range and load-carrying ability are still unmatched by newer aircraft in the fleet.

The eight prototypes and pre-production Intruder aircraft were sometimes referred to with the YA-6A designation.[15] These were used in the development and testing of the A-6A Intruder.

The initial version of the Intruder was built around the complex and advanced DIANE (Digital Integrated Attack/Navigation Equipment), intended to provide a high degree of bombing accuracy even at night and in poor weather. DIANE consisted of multiple radar systems: the Norden SystemsAN/APQ-92 search radar replacing the AN/APQ-88 on YA-6A, and a separate AN/APG-46 for tracking, AN/APN-141 radar altimeter, and AN/APN-122 Doppler navigational radar to provide position updates to the Litton AN/ASN-31 inertial navigation system. An air-data computer and the AN/ASQ-61 ballistics computer integrated the radar information for the bombardier/navigator (BN) in the right-hand seat. TACAN and ADF were also provided for navigational use. When it worked, DIANE was perhaps the most capable nav/attack system of its era, giving the Intruder the ability to fly and fight in even very poor conditions (particularly important over Vietnam and Thailand during the Vietnam War). It suffered numerous teething problems, and it was several years before its reliability was established.

A-6B on the USS Saratoga in 1971

Total A-6A production was 480, excluding the prototype and pre-production aircraft.[15] A total of 47 A-6As were converted to other variants.[15]

To provide U.S. Navy squadrons with a defense suppression aircraft to attack enemy antiaircraft defense and SAM missile systems, a mission dubbed "Iron Hand" by the U.S. Navy, 19 A-6As were converted to A-6B version during 1967 to 1970.[15] The A-6B had many of its standard attack systems removed in favor of specialized equipment to detect and track enemy radar sites and to guide AGM-45 Shrike and AGM-78 Standardanti-radiation missiles, with AN/APQ-103 radar replacing earlier AN/APQ-92 used in the A-6A, plus AN/APN-153 navigational radar replacing earlier AN/APN-122, again used in the A-6A.

Between 1968 and 1977, several Intruder squadrons operated A-6Bs alongside their regular A-6As. Five were lost to all causes, and the survivors were later converted to A-6E standard in the late 1970s.

12 A-6As were converted in 1970 to A-6C standard for night attack missions against the Ho Chi Minh Trail in Vietnam. They were fitted with a "Trails/Roads Interdiction Multi-sensor" (TRIM) pod in the fuselage for FLIR and low-light TV cameras, as well as a "Black Crow" engine ignition detection system. Radars were also upgraded, with AN/APQ-112 replacing earlier AN/APQ-103 in A-6B, and AN/APN-186 navigational radar replacing earlier AN/APN-153 in earlier A-6B. A vastly improved Sperry Corporation AN/APQ-127 radar replaced earlier AN/APG-46 fire control radar in A-6A/B. One of these aircraft was lost in combat, the others were later converted to A-6E standard after the war.

To replace both the KA-3B and EA-3B Skywarrior during the early 1970s, 78 A-6As and 12 A-6Es were converted for use as tanker aircraft, providing aerial refueling support to other strike aircraft. The DIANE system was removed and an internal refueling system was added, sometimes supplemented by a D-704 refueling pod on the centerline pylon. The KA-6D theoretically could be used in the day/visual bombing role, but it apparently never was, with the standard load-out being four fuel tanks. Because it was based on a tactical aircraft platform, the KA-6D provided a capability for mission tanking, the ability to keep up with strike packages and refuel them in the course of a mission. A few KA-6Ds went to sea with each Intruder squadron. Their operation was integrated into the Intruder squadrons, as A-6 crew were trained to operate both aircraft and the NATOPS covered both the A6 and KA-6D. These aircraft were always in short supply, and frequently were "cross decked" from a returning carrier to an outgoing one. Many KA-6 airframes had severe G restrictions, as well as fuselage stretching due to almost continual use and high number of catapults and traps. The retirement of the aircraft left a gap in USN and USMC refueling tanker capability. The USN Lockheed S-3 Viking also had an aerial refueling capability, but its performance and fuel capacity effectively limited it to the role of recovery tanker. The loss of mission tanking capability was only later remedied by the new F/A-18E/F Super Hornet, which can act as a mission tanker.

The definitive attack version of the Intruder with vastly upgraded navigation and attack systems, introduced in 1970 and first deployed on 9 December 1971. The earlier separate search and track (fire control) radars of the A-6A/B/C were replaced by a single Norden AN/APQ-148 multi-mode radar, and onboard computers with a more sophisticated (and generally more reliable) IC based system, as opposed to the A-6A's DIANE discrete transistor-based technology. A new AN/ASN-92 inertial navigation system was added, along with the CAINS (Carrier Aircraft Inertial Navigation System), for greater navigation accuracy.

Beginning in 1979, all A-6Es were fitted with the AN/AAS-33 DRS (Detecting and Ranging Set), part of the "Target Recognition and Attack Multi-Sensor" (TRAM) system, a small, gyroscopically stabilized turret, mounted under the nose of the aircraft, containing a FLIR boresighted with a laser spot-tracker/designator and IBMAN/ASQ-155 computer. TRAM was matched with a new Norden AN/APQ-156 radar. The BN could use both TRAM imagery and radar data for extremely accurate attacks, or use the TRAM sensors alone to attack without using the Intruder's radar (which might warn the target). TRAM also allowed the Intruder to autonomously designate and drop laser-guided bombs. In addition, the Intruder used Airborne Moving Target Indicator (AMTI), which allowed the aircraft to track a moving target (such as a tank or truck) and drop ordnance on it even though the target was moving. Also, the computer system allowed the use of Offset Aim Point (OAP), giving the crew the ability to drop on a target unseen on radar by noting coordinates of a known target nearby and entering the offset range and bearing to the unseen target.

In the 1980s, the A-6E TRAM aircraft were converted to the A-6E WCSI (Weapons Control System Improvement) version to add additional weapons capability. This added the ability to carry and target some of the first generation precision guided weapons, like the AGM-84 Harpoon missile, and AGM-123 Skipper. The WSCI aircraft was eventually modified to have a limited capability to use the AGM-84E SLAM standoff land attack missile. Since the Harpoon and SLAM missiles had common communication interfaces, WCSI aircraft could carry and fire SLAM missiles, but needed a nearby A-6E SWIP to guide them to target.

In the early 1990s, some surviving A-6Es were upgraded under SWIP (Systems/Weapons Improvement Program) to enable them to use the latest precision-guided munitions, including AGM-65 Mavericks, AGM-84E SLAMs, AGM-62 Walleyes and the AGM-88 HARManti-radiation missile as well as additional capability with the AGM-84 Harpoon. A co-processor was added to the AN/ASQ-155 computer system to implement the needed MIL-SPEC 1553 digital interfaces to the pylons, as well as an additional control panel. After a series of wing-fatigue problems, about 85% of the fleet was fitted with new graphite/epoxy/titanium/aluminum composite wings. The new wings proved to be a mixed blessing, as a composite wing is stiffer and transmits more force to the fuselage, accelerating fatigue in the fuselage. In 1990, the decision was made to terminate production of the A-6. Through the 1970s and 1980s, the A-6 had been in low-rate production of four or five new aircraft a year, enough to replace mostly accidental losses. The final production order was for 20 aircraft of the SWIP configuration with composite wings, delivered in 1993.

A-6E models totaled 445 aircraft, about 240 of which were converted from earlier A-6A/B/C models.

An advanced A-6F Intruder II was proposed in the mid-1980s that would have replaced the Intruder's elderly Pratt & Whitney J52turbojets with non-afterburning versions of the General Electric F404turbofan used in the F/A-18 Hornet, providing substantial improvements in both power and fuel economy. The A-6F would have had totally new avionics, including a Norden AN/APQ-173synthetic aperture radar and multi-function cockpit displays – the APQ-173 would have given the Intruder air-to-air capacity with provision for the AIM-120 AMRAAM. Two additional wing pylons were added, for a total of seven stations.

Although five development aircraft were built, the U.S. Navy ultimately chose not to authorize the A-6F, preferring to concentrate on the A-12 Avenger II. This left the service in a quandary when the A-12 was canceled in 1991.

Grumman proposed a cheaper alternative in the A-6G, which had most of the A-6F's advanced electronics, but retained the existing engines. This, too, was canceled.

US Marine Corps EA-6A Intruder electronics aircraft of VMCJ-2 Playboys aboard USS America in 1974 during a visit to Scotland.

An electronic warfare (EW)/Electronic countermeasures (ECW) version of the Intruder was developed early in the aircraft's life for the USMC, which needed a new ECM platform to replace its elderly F3D-2Q Skyknights. An EW version of the Intruder, initially designated A2F-1H (rather than "A2F-1Q" as "Q" was being split to relegate "Q" to passive and "H" to active electronic warfare) and subsequently redesignated EA-6A, first flew on 26 April 1963. It had a Bunker-Ramo AN/ALQ-86 ECM suite, with most electronics contained on the walnut-shaped pod atop the vertical fin. They were equipped with AN/APQ-129 fire control radar, and theoretically capable of firing the AGM-45 Shrikeanti-radiation missile, although they were apparently not used in that role. The navigational radar is AN/APN-153.

Only 28 EA-6As were built (two prototypes, 15 new-build, and 11 conversions from A-6As), serving with U.S. Marine Corps squadrons in Vietnam. It was phased out of front line service in the mid-1970s, remaining in use in reserve VMCJ units with the USMC and then the United States Navy in specialized VAQ units, primarily for training purposes. The last EA-6A had been retired by 1993.

A much more highly specialized derivative of the Intruder was the EA-6B Prowler, having a "stretched" airframe with two additional systems operators, and more comprehensive systems for the electronic warfare and SEAD roles. A derivative of AN/APQ-156, AN/APS-130 was installed as the main radar for EA-6B. The navigational radar was upgraded to AN/APS-133 from the AN/APN-153 on EA-6A. In total, 170 were produced. The EA-6B took on the duties of the U.S. Air Force EF-111 Raven when the DoD decided to let the U.S. Navy handle all electronic warfare missions. The Prowler remains in service as of 2012, but is being replaced by the EA-18G Growler in the U.S. Navy. The U.S. Marine Corps does not intend to acquire the EA-18G and will continue to operate the EA-6B for the near future, acquiring some U.S. Navy EA-6Bs as they are replaced by the EA-18G.

Electronic warfare variant redesignated from A2F-1H, had a redesigned fin and rudder and addition of an ECM radome, able to carry underwing ECM pods, three YA-6A and four A-6As converted and 21 built.[17]

NA-6A

The redesignation of three YA-6As and three A-6As. The six aircraft were modified for special tests.[17]

The A-6 Intruder was featured in a 1986 novel by Stephen Coonts called Flight of the Intruder , with a plot line somewhat similar to the book Thud Ridge about pilots flying into Hanoi restricted by militarily dubious rules of engagement. In 1991, Flight of the Intruder was adapted as a motion picture, and followed by the novel's 1995 sequel, The Intruders.

^Hildebrandt, Erik. 1996–1997. "Burial at Sea: Navy's A-6 Intruder is Retiring, and What Could be a More Fitting End?" Air and Space Smithsonian. December 1996 – January 1997, Volume 11 (5). Pages 64–70. Also: "Burial at Sea."

Hildebrandt, Erik. 1996–1997. "Burial at Sea: Navy's A-6 Intruder is Retiring, and What Could be a More Fitting End?" Air and Space Smithsonian. December 1996 – January 1997, Volume 11 (5). Pages 64–70. Also: "Burial at Sea."